Spike Jonze has a knack for disturbing our peace, and his new film "Her" does that with a vengeance.

A different and daring futuristic tale starring Joaquin Phoenix and Scarlett Johansson, "Her" is a look at the pleasures and perils of new technology that's a smart entertainment and a subtle warning, a love story and a horror show. Acerbic, emotional, provocative, it's a risky high dive off the big board with a plot that sounds like a gimmick but ends up haunting, odd and a bit wonderful.

Previously responsible for the singular "Being John Malkovich" and "Adaptation" as well as the self-indulgent "Where the Wild Things Are," Jonze is a director who goes his own way with ideas no one else could have imagined.

With "Her," Jonze for the first time has sole writing credit. He not only came up with a killer idea, he's had the nerve to go all the way with it, to tease out multiple implications of his lightly dystopian "what if" plot all the way to the unforeseen but perfectly logical denouement.

What helps Jonze get the most out of his examination of the consequences of a man (Phoenix) falling in love with the voice of his operating system (Johansson, never seen on-screen) is his lack of interest in making "Her" simply an empty Luddite screed.

As Jonze has taken pains to insist in numerous interviews, "Her" in his mind is as much about the nature of individual relationships as it is about a future in which we trust and rely on our devices more than we do our fellow human beings.

"Her's" fascination with the pending impersonalization of the personal, with a coming world where falsity is the new sincerity, begins with its first sequence, which has Phoenix's Theodore looking directly at the camera and saying with genuine feeling, "I've been thinking of telling you how much you mean to me."

The succeeding dialogue, however, reveals that Theodore is not being emotional, he's just doing his job, working for BeautifulHandwrittenLetters.com, a company that makes it its business to compose personal thank you notes for the gratitude impaired.

This slightly futuristic enterprise is set in a slightly futuristic Los Angeles, evocatively photographed by Hoyte Van Hoytema ("Tinker Tailor Soldier Spy") and smartly constructed out of bits of the real Los Angeles and glimpses of Shanghai's new purpose-built Pudong district by the directors' longtime production designer K.K. Barrett.

With glasses and a diffident manner typing him as a bit of a nerd, Theodore doesn't quite know what to do with himself when he's alone, which is a lot of the time. "Her" gives him a number of options, including unnerving phone sex, happy flashback memories of his former marriage to Catherine (Rooney Mara, softer than we're used to) and a video game featuring a foul-mouthed alien tot (Jonze provides the unnerving voice.)

Phoenix does solid work in this poor soul role, but, not surprising for an actor who is most at home with extreme characters like Freddie Quell in "The Master," he becomes more convincing once "Her" ventures into stranger territory. Once, in other words, Samantha comes into Theodore's life.

It all starts with an ad that catches Theodore's eye, an ad promising "the first artificially intelligent operating system ... a consciousness that knows you." With nothing else going on in his life, Theodore is ready for something new, so he signs on.

Enter Samantha, with a voice that tells you immediately that this is an entity who really cares about you, you and only you. Theodore is nonplused at first by Samantha's easy familiarity. But he soon gets used to "her" and, given what she brings to his life, that is no surprise.

In short order — Samantha is nothing if not a quick study — she organizes Theodore's schedule, helps him with his writing and his video game playing, laughs at his jokes and makes some of her own. Samantha also encourages him to seek human companionship beyond his old college pal Amy (a very different Amy Adams from her flashy con woman in "American Hustle"), even pushing him into a problematic blind date (an impressive Olivia Wilde.) Is it any wonder that Theodore is soon telling Samantha that he has more fun with her than anyone ... human?

Key to making this transition work is the exceptional work done by Johansson in a part that was originally acted from start to finish by Samantha Morton before Jonze decided he wanted a different vocal quality in the role. Johansson does a remarkable job using only her voice to create what is in effect a brand new person whose warmth and joy are infectious.

Samantha doesn't stay brand new for long, however. As Theodore gets increasingly attached to her, Samantha is learning more and more about what human life is like. "I have intuition, the ability to grow and evolve through my experiences, just like you" she is continually reminding Theodore, but she is learning at an exponential rate, which leads to problems and situations only Jonze could think up and bring off.

As the relationship deepens, Jonze draws intriguing parallels between the Theodore-Samantha relationship, alternately creepy and sweet, and one between two actual people. If falling in love with anyone is a form of socially acceptable insensitivity, someone asks, how is what these two have that much different?

Finally, however, the questions "Her" poses about the ambivalent potential of personal technology is its most intriguing aspect. This is a film about how we live now and how we might live in the future. We are entering a brave new world and dealing with the consequences is our fate.